From: Helge Deller <deller@gmx.de>
Date: Thu, 4 Jun 2015 21:57:18 +0000 (+0200)
Subject: compat: cleanup coding in compat_get_bitmap() and compat_put_bitmap()
X-Git-Tag: omap-for-v4.3/legacy-v2-signed~266
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9b7b819ca1e508195feed5ece558dca66adeef05;p=pandora-kernel.git

compat: cleanup coding in compat_get_bitmap() and compat_put_bitmap()

In the functions compat_get_bitmap() and compat_put_bitmap() the
variable nr_compat_longs stores how many compat_ulong_t words should be
copied in a loop.

The copy loop itself is this:
  if (nr_compat_longs-- > 0) {
      if (__get_user(um, umask)) return -EFAULT;
  } else {
      um = 0;
  }

Since nr_compat_longs gets unconditionally decremented in each loop and
since it's type is unsigned this could theoretically lead to out of
bounds accesses to userspace if nr_compat_longs wraps around to
(unsigned)(-1).

Although the callers currently do not trigger out-of-bounds accesses, we
should better implement the loop in a safe way to completely avoid such
warp-arounds.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
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